Insert for drill bit and manufacture thereof

ABSTRACT

A solid wear-resistant sintered metallic carbide insert adapted for forcible insertion into an opening in a working face of a drill bit includes a generally polygonal body portion having at least about 12 sides extending between opposite ends thereof, and a heat portion on one end of the body portion, the corners formed by the said sides being abraded at the ends of the body portion and tapering inwardly towards the end of the body portion opposite to the said one end thereof, the body portion being insertable into the working face opening for mounting the body portion therein with the head portion exposed at the working face. A drill bit incorporating the insert includes a body having a working face provided with a plurality of generally circular insert openings extending inwardly therefrom, and a plurality of the inserts mounted in the openings, each insert engaging the wall of the opening in which mounted in an interference fit. A method of making the insert includes the steps of molding metallic carbide powder under die pressure to form a molded article including a generally polygonal body portion having at least about 12 sides extending between opposite ends thereof and a head portion on one end of the body portion, the body portion tapering inwardly towards the end thereof opposite to the said one end, sintering the molded article to form a sintered article having concave sides, and abrading the sintered article whereby the corners formed by the sides are abraded at the ends of the body portion and are tapered inwardly towards said opposite end of the body portion, thereby producing an insert having the body portion insertable into the working face opening for mounting the body portion therein with the head portion exposed at the working face.

United States Patent [72} Inventor Frank E. Stebley 3815 Nemesis,Gurnee, 111. 60031 [211 App]. No. 822,883 [22] Filed May 8, 1969 [45]Patented June 1, 1971 [54] INSERT FOR DRILL BIT AND MANUFACTURE THEREOF9 Claims, 9 Drawing Figs.

[52] U.S. Cl 175/409, 76/108 [51] Int. Cl E2lc 13/00 [50] Field ofSearch 175/409, 410,41 1, 374; 76/108 [56] References Cited UNITEDSTATES PATENTS 2,121,202 6/1938 Killgore 175/374 2,673,716 3/1954 Avery175/411 2,687,875 8/1954 Morlan et a1. 175/410X 3,071,201 1/1963 Phipps175/410 3,356,418 12/1967 Healey et al.. 175/411 3,382,940 5/1968Stebley 175/410 FOREIGN PATENTS 984,597 2/1951 France 175/410 PrimaryExaminerMarvin A. Champion Assistant Examiner-Richard E. FavreauAttorney-John S. OBrien ABSTRACT: A solid wear-resistant sinteredmetallic carbide insert adapted for forcible insertion into an openingin a working face ofa drill bit includes a generally polygonal bodyportion having at least about 12 sides extending between opposite endsthereof, and a heat portion on one end of the body portion, the comersformed by the said sides being abraded at the ends of the body portionand tapering inwardly towards the end of the body portion opposite tothe said one end thereof, the body portion being insertable into theworking face opening for mounting the body portion therein with the headportion exposed at the working face. A drill bit incorporating theinsert includes a body having a working face provided with a pluralityof generally circular insert openings extending inwardly therefrom, anda plurality of the inserts mounted in the openings, each insert engagingthe wall of the opening in which mounted in an interference fit.

A method of making the insert includes the steps of molding metalliccarbide powder under die pressure to form a molded article including agenerally polygonal body portion having at least about 12 sidesextending between opposite ends thereof and a head portion on one end ofthe body portion, the body portion tapering inwardly towards the endthereof opposite to the said one end, sintering the molded article toform a sintered article having concave sides, and abrading the sinteredarticle whereby the corners formed by the sides are abraded at the endsof the body portion and are tapered inwardly towards said opposite endof the body portion, thereby producing an insert having the body portioninsertable into the working face opening for mounting the body portiontherein with the head portion exposed at the working face.

PATE-NTED'JUN 1 91: 3581.835

SHEET 2 BF 2 A h soa L 60 so 52 FIG.7 so

' FIGS 92 INVENTOR FRANK E. STEBLEY ATTORNEY INS RT Eon DRILL BIT ANDMANUFACTURE THEREOF BACKGROUND OF THE INVENTION This invention relatesto a solid wear-resistant sintered metallic carbide insert adapted forforcible insertion into an opening in a working face of a drill bit, adrill bit incorporating the insert, and a method making the insert. Moreparticularly, the invention relates to an insert which may be mounted inimperfectly shaped openings in a drill bit with reduced insert fractureand loss in drilling, and to a method of making the insert in asimplified manner as compared to prior methods.

Inserts or teeth of wear-resistant sintered metallic carbide are widelyused in drill bits for earth-drilling tools, especially for drillinginto rock formations. Such inserts have much greater wearability thansimilar inserts constructed of steel. While hard and wear-resistant, thecarbide inserts are also brittle and have poor resistance to bending.Consequently, the inserts have a tendency to break in use when notproperly mounted in the drill bit, and they may also be lost from thebit. Inasmuch as the inserts cannot be replaced in many drill bits, itbecomes necessary eventually to discard the entire bit, which is verycostly.

A popular type of percussion drill bit is constructed of a solid steelbody having a working face or faces at one end of the bit, and aplurality of generally cylindrical inserts or teeth of sintered metalliccarbide which are mounted in openings in the working face and areexposed thereat. The inserts are similarly employed in roller cone andother types of drill bits for penetrating earth formations by impact andcutting action, and also for minimizing drill bit wear. The inserts areforcibly inserted into openings having slightly smaller diameters thanthe insert diameter, so that the inserts engage the walls of theopenings in which mounted in an interference fit.

Owing to the brittle nature of the carbide inserts, they should beprovided with maximum support by the steel bit body when mounted. Withpoor support, especially adjacent he face of the bit, the inserts areprone to fracture under transverse forces, and they may also work looseand fall out of the bit. In manufacturing a suitable bit body, the steelstructure usually is drilled to provide insert openings and thenheattreated to a predetermined degree of hardness. The drilled holesthen are precisely reamed to correct for heat distortion and drillingerrors, and form insert openings or holes having the desired diameterand cylindrical configuration.

The carbide inserts are manufactured by molding metallic carbide powderunder die pressure to form oversize molded articles. The molded articlesare sintered to form solid sintered articles having the desired physicalproperties. Inasmuch as the molded articles are compressed between diesacting at opposite ends of the articles, the density or compression ofthe material varies from a maximum adjacent the ends to a minimum in thecentral region. The sintering step is accompanied by shrinkage, whichincreases towards the less dense central region, so that the resultingarticles have generally concave sides. For example, the shrinkage in aninsert of about five-eighths inch diameter and about 1 inch length isgenerally about 0.003 to 0.004 inch at the center. Consequently, theinserts are ground to eliminate the concavity and provide cylindricalbodies of the desired diameter. Thereafter, the inserts may be tumbledin an abrasive medium to abrade or round off their corners.

The finished inserts are pressed into the openings in the drill bit toseat them firmly in the openings, with the outer ends or head portionsof the inserts exposed at the working face, from which they project forimpacting and cutting action. Inserts provided for minimizing the wearof the bit may lie flush with the face of the bit or project lesserdistances therefrom.

Careful insertion of the inserts into their openings is necessary, toavoid distortion of the openings which would reduce the gripping force.Inasmuch as the resiliency of the steel bit body is limited, a portionof the gripping force may be lost during mounting of the inserts.Drilling errors that survive the reaming operation most frequentlyresult in the insert openings having greater diameters at the top thanat the bottom. Openings may be noncircular at the top, or suffer from abell-mouth condition. Consequently, the inserts are gripped mostsecurely at the bottom and to lesser degrees in the center and upper orouter areas. Theinserts then are more prone to fracture in theiropenings, and to loosening with eventual loss.

It would be highly advantageous to provide a Wear-resistant sinteredmetallic carbide insert that may be securely mounted in an opening in aface of a drill bit despite imperfections in the size and shape of theopening as commonly encountered in practice. It would also beadvantageous to provide a relatively simple method of making such aninsert.

SUMMARY OF THE INVENTION The present invention provides a new andimproved solid wear-resistant sintered metallic carbide insert adaptedfor forcible insertion into an opening in a working face of a drill bitto obviate or minimize the problems previously occasioned byimperfections in the openings and provide a drill bit having insertssecurely mounted therein and resistant to fracture and end of the bodyportion, the corners formed by the sides being abraded at the ends ofthe body portion and tapering inwardly towards the end of the bodyportion opposite to the head end, the body portion being insertable intoa working face opening for mounting the body portion therein with thehead portion exposed at the working face. The preferred metallic carbidecomprises tungsten carbide. The body portion preferably is provided withabout 12 to 20 sides in the insert sizes most commonly employed.

The new insert preferably also includes a seat portion having a beveledperipheral edge on the end of the body portion opposite to the head end,the corners formed by the edge being abraded, and the seat portion beingseated on the bit at the base of the working face opening when the bodyportion is mounted therein.

The invention provides a drill bit including a body having a workingface provided with a plurality of generally circular insert openingsextending inwardly therefrom, and a plurality of the inserts mounted intee openings, each insert engaging the wall of the opening in whichmounted in an interference fit.

The new method of the invention includes the steps of molding metalliccarbide powder under die pressure to form a molded article including agenerally polygonal body portion having at least about 12 sidesextending between opposite ends thereof and a head portion on one end ofthe body portion, the'body portion tapering inwardly towards the endopposite to the one end, sintering the molded article to form a sinteredarticle having concave sides, and abrading the sintered article wherebythe corners formed by the sides are abraded at the ends of the bodyportion and are tapered inwardly towards the end thereof opposite thehead end, thereby producing an insert having the boy portion insertableinto a working face opening for mounting the body portion therein withthe head portion exposed at the working face. In a preferred embodimentof the invention, the sintered article is abraded by tumbling in anabrasive medium.

The new insert is constructed for overcoming the errors which commonlyoccur in drilling insert openings in a drill bit face, without need forthe usual reaming operation to provide a precise hold size and shape.When mounted in the drill bit, the insert is supported securely from topto bottom, thereby resisting bending and torsional stresses, andfracture and loss of inserts are prevented.

The new insert is made by a method which embodies generally conventionalmolding and sintering steps followed merely by an abrading step thatdispenses with prior precision grinding.

BRIEF DESCRIPTION OF THE DRAWINGS The attached drawings illustratepreferred embodiments of the invention, without limitation thereto. lnthe drawings, like elements are identified by like reference symbols ineach of the views, and:

FIG. 1 is a partly sectional fragmentary view ofa rotary-percussiondrill bit incorporating inserts constructed according to the invention;

FIG. 2 is an enlarged fragmentary sectional view of a die assemblyemployed in making molded articles for sintering according to the newmethod of the invention;

FlG. 3 is a view similar to FlG. 2 but illustrating the moldedoperation;

FIG. 4 is a further enlarged view ofa molded article made as illustratedin FlG. 3;

FIG. 5 is a top plan view on a still larger scale of one quadrant of thearticle of FIG. 4, representative also the remainder of the article;

FIG. 6 is an elevational view of the article illustrated in FIG. 4 aftersintering the article, drawn to the same scale and with the sidecurvature thereof exaggerated for illustrative purposes;

FIG. 7 is an enlarged elevational view of the sintered article after ithas beenabraded, thus providing an insert constructed according to apreferred embodiment ofthe invention;

FIG. 8 is an elevational view of an insert representing anotherembodiment of the invention, drawn to the scale of FIG. 6, wherein thehead portion of the insert is enlarged relative to the insert of FIG. 7;and

FlG. 9 is an elevational view on the same scale of an insert accordingto a further embodiment of the invention, wherein the insert is providedwith a head portion having a different configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, FIG.1 illustrates a rotary-percussion drill bit 10 incorporating a pluralityof solid wear-resistant sintered metallic carbide inserts 12 accordingto the invention. The inserts 12 are illustrated in greater detail inFlG. 7. An optional insert 14 is also illustrated in HO. 1, in brokenlines.

The illustrative drill bit 10 includes a conventional bit body 16, ofwhich only the impact end 18 is illustrated. In the complete structure,a shank is integral with the impact end and serves for connection to adrilling tool including passage means for supplying water or other fluidto the bit body 16. The impact end 18 includes a slightly taperedfrustoconical outer base portion 20, and an inner frustoconicalconnecting portion 22 joining the base portion to the shank of the bitbody. The bit body is provided with a central longitudinal fluidpassageway 24 communicating with branch passageways 26 which dischargeflushing fluid from the base portion 20. Longitudinal grooves 28 in thesurface of the bit body 16 provide return passageways for fluid andcutting removed from the bottom of a hole being drilled in a formation.Working faces or surfaces are provided by the base portion of the bitbody 16, including a transverse end face 30 on the bottom of the bit, aside face 32 extending upwardly and slightly inwardly from the end face,and a corner face 34 at an angle to the end face 30 around the peripheryof the base portion. The end face 30 and the comer face 34 are providedwith generally cylindrical insert openings or holes 36 and 38,respectively, which extend inwardly from the faces. The holes aredefined by generally circular walls 40 and shallow conical bottomsurfaces 42 as formed by the drill bit. The bottom surfaces 42 extend atangles of about 60 to the longitudinal axes of the openings 36 and 38.The inserts 12 are mounted in the openings 36 and 38, each insertengaging a wall 40 in an interference fit and being seated on a bottomsurface 42 at the base of an opening.

In the illustrative bit 10, fragmentation of formation is effectedprincipally at the end face 30 and the corner face 34. The insert 14 andother similar inserts are optionally provided in the side face 32 tomaintain the gauge of the bit. Alternatively, inserts providingadditional cutting action may be mounted in the side face 32 or othercorresponding structure. Representative such structure is illustrated inmy US. Pat. No. 3,382,940, wherein the impact end of the bit includes aseparable head. Likewise, the present invention may be applied to adrill bit otherwise constructed like the drill bit of such patent, todrill bits of the rolling cutter type, and to other drill bits fordrilling or boring into hard earth formations.

The bit body 16 is a solid steel body having the described passageways,grooves and openings. The bit body is con structed so that its hardnessvaries, being softer adjacent the working faces 30, 32 and 34 where theinserts are mounted, and being harder behind the inserts. There is ahardness transition zone between the two regions of the body. Theinserts 12, and other illustrative inserts, preferably are formed oftungsten carbide, also referred to as cemented tungsten carbide. Whilesuch carbide is preferred, other carbide compositions might be employedwhere desirable, such as tantalum carbide, which however produces a morebrittle insert.

Referring to FIG. 7, the insert 12 includes a generally polygonal bodyportion 44 having a plurality of sides 46 of uniform width extendingbetween opposite ends thereof. A hemispherical head portion 48 isintegral with the body portion 44 on one end of the latter. A circularseat portion 50 having a beveled peripheral edge 52 is integral with thebody portion 44 on the opposite end thereof. The circular base of thehemispherical head portion 48 is substantially tangent to the sides 46,as illustrated in FIG. 5 for the presintered molded article 12, showingthe head portion 48 tangent to the sides 46' thereof. Likewise, thecircular base of the seat portion 50 is substantially tangent to thesides 46.

The corners 54 formed by the body portion sides 46 are abraded orrounded increasingly from about the central region 56 of the bodyportion to the opposite ends thereof, where relatively long radiusabraded or rounded corner surfaces 58 and 60 are provided. Theperipheral edge 52 of the seat portion 50 forms corners with the sides46 and the bottom of the seat portion, and such corners also are abradedor rounded.

In the illustrative structure, the abraded corner surfaces 58 and 60 mayproject slightly beyond adjacent surfaces of the head portion 48 and theseat portion 50, as illustrated by the abraded surfaces 58a and 601:shown in profile. The degree of projection may vary, and the abradedsurfaces 58 and 60 may be substantially flush with such adjacentsurfaces. The corners 54 taper inwardly at a small angle to thelongitudinal axis of the insert, towards the end of the body portion 44bearing the seat portion 50. The areas of the sides 46 between thecorners 54 are slightly concave.

Referring to FIGS. 2 and 3, manufacture of the insert 12 according tothe invention is initiated in a generally conventional mold assembly 62.The assembly includes a mold body 64 having a mold cavity 66 therein,and upper and lower dies 68 and 70. Pursuant to the invention, the wallsof the mold cavity 66 are provided with a polygonal wall section 72having a slight inward taper from top to bottom. The upper die 68 isprovided with a hemispherical cavity 74. The lower die 70 is providedwith a shallow frustoconical cavity 76. The cavities 74 and 76 havecircular openings at their inner ends which are substantially tangent tothe sides 78 of the polygonal wall section 72.

FIG. 2 illustrates the dies 68 and 70 in withdrawn position preparatoryto filling and closing the mold assembly 62. HO. 3 illustrates the moldassembly 62 as it appears when filled with metallic carbide powder 79under the pressure of the dies 68 and 70. It will be noted that the diepressure is exerted at the opposite ends of the article being formed,which results in greater compression and density adjacent the ends andlesser compression and density in the direction of the longitudinalcenter of the molded article. The taper provided by the polygonal wallsection 72 serves both for ejection of the molded article at the top ofthe mold cavity 66, and for producing an article and ultimately theinsert 12 having a functionally desirable taper, as describedhereinafter.

The product of the molding operation illustrated in FIGS. 2 and 3 is themolded article 12' illustrate in FIGS. 4 and 5. This article includes agenerally polygonal body portion 44 having sides 46 extending betweenopposite ends thereof and forming corners 54', a hemispherical headportion 48' on one end of the body portion, and a frustoconical seatportion 50' having a beveled or chamfered peripheral edge 52 on theopposite end of the body portion. The edge 52 extends at an angle of 60to the longitudinal axis of the molded article. The bases or innerportions of the head portion 48' and the seat portion 50' are circularand substantially tangent to the sides 46' within the polygon defined bythe body portion 44'. The body portion tapers inwardly towards the endbearing the seat portion 50.

The molded article 12' is sintered in a conventional manner to produce asolid wear-resistant sintered metallic carbide article 12", illustratedin FIG. 6, which may be abraded to produce the desired insert 12,illustrated in FIG. 7. The sintering operation is accompanied by adegree of shrinkage. Owing to the decrease in density in the moldedarticle 12', from the ends of the body portion 44' to the central region56' thereof, the sides 46" of the sintered article 12" are slightlyconcave, as illustrated.

In the past, when conventional inserts were made generally in theforegoing manner, the sintered articles were ground in a close toleranceoperation to eliminate the concavity and accurately determine thediameter of the insert. Thereafter, they were tumbled in an abrasivemedium for a limited time suffcient to remove any scale, impart a finer,smoother surface to the insert, and remove the sharp corners on theinsert.

in the present invention, the sintered article 12", without grinding, isabraded for an extended period of time, e.g., about 8 to 10 hours oftumbling in an abrasive medium, sufficient to abrade the corners 54",especially at the ends of the body portion 44". The most prominentsurfaces are abraded to the greatest extent. Consequently, the ends ofthe corners 54"adjacent the head portion 48" and the seat portion 50",are abraded or radiused to a substantial extent, whereas theintermediate segments of the corners 54" are abraded to a lesser degreetowards the central region 56". Thus, the corners 54" are abraded orrounded increasingly from about the central region 56" of the bodyportion to the ends thereof. In this manner, the abraded corner surfaces58 and 60 and progressively smaller abraded comer surfaces are providedon the body portion 44, as illustrated in FIG. 7.

Abrasion of the comers 54" of the sintered article 12" in this mannerresults in the corners 54 of the insert 12 being tapered inwardlytowards the seat portion 50, similarly to the taper of the body portion44' of the molded article 12'. The

. portions of the sides 46 of the insert 12 between the ends of the bodyportion 44 will retain the concavity of the sintered article sides 46",inasmuch as they are abraded to a substantial extent only adjacent theends of the body portion. The extent to which the abraded cornersurfaces 58 and 60 project from the head and seat portions 48 and 50will depend upon the time and conditions of abrasion, which aresufficient to provide the desired taper in the corners 54. The degree ofprojection will also depend upon the number of sides 46, diminishingwith an increasing number of sides. At times, the abraded surfaces 58and 60 may be substantially flush at their ends with the head and seatportions 48 and 50.

The corners formed by the seat portion 50" of the sintered article alsoare abraded, so that the beveled peripheral edge 52 on the insert 12becomes rounded, as illustrated in FIG. 7. At the same time, theadjacent edges of the side corner surfaces 60 may be abraded to mergewith the edge 52.

The abrading operation preferably is conducted by barreltumbling in anabrasive medium, in a conventional manner. The operation issometimes'referred to as prehoning" when applied to cutting inserts forshop tools. An effective medium includes aluminum oxide and silicon rockwetted with a basarwater solution. Alternatively, the inserts may firstbe gritblasted while set on end in a rubber mat or other holder,exposing their opposite ends alternately, to hasten the abrasion. Suchabrasion is followed by tumbling in an abrasive medium to provide thedesired smooth finish.

FIG. 8 illustrates another embodiment of the insert of the invention.This structure is provided with an enlarged hemispherical head portion82. The adjacent end 84 of the insert body portion 86 is tapered orinclined at a greater angle to the longitudinal axis of the insert,corresponding to the enlarged diameter of the head portion. Thisstructure is advantageous for mounting in drill bit openings whichsuffer from a bellmouth condition around the rims of the openings at theworking face. With suitable modification of the mold assembly 62 shownin FIGS. 2 and 3, the insert 80 is made in the same manner as theforegoing insert 12.

FIG. 9 illustrates an insert 90 having a head portion 92 offrustoconical configuration on a body portion 94 like the body portion44 of the above-described insert 12. The insert 90 might be preferred,for example, for use as the optional insert 14 illustrated in the sideface 32 of the drill bit 10 in FIG. 1. Similarly, various other headportion configurations might be substituted where desirable. Except forappropriate changes in the die cavity for molding, the manufacture ofthe insert 90 or inserts having other head portions is as describedabove for the insert 12.

Referring to the insert 12 shown in FIGS. 1 and 7 as illustrative, thebody portion 44 of the insert is insertable into the openings 36 and 38in the working faces 30 and 34 for mounting the body portion thereinwith the beveled edge 52 of the seat portion 50 seated on thecorrespondingly angled bottom surface 42 of each opening and the headportion 48 exposed at the working face and, in these instances,projecting outwardly therefrom. ln pressing the insert into an opening,the tapered construction and the rounded seat portion 50 assist inproperly locating the insert in the opening without disturbing theopening or scraping the sidewall 40. As the tapered body portion 44 isinserted, the corners 54 wedge into the sidewall 40 and correct fordrilling errors. The steel of the bit body may conform to theconfiguration of the polygon. Engagement of the corners 54 serves toprevent turning of the insert when subjected to torsional forces, andprevent axial movement of the insert. The tapered construction serves towedge the insert in the opening not only towards the bottom of the wall40, where drilling errors may be slight, but also at the middle andupper or outer areas of the wall 40, where the opening is more likely tosuffer from imperfections such as widening, out-ofround, and loss ofresiliency.

As the body portion 44 is inserted, the wedging pressure of the corners54 is increased from the central region 56 to the widening abradedcorner surfaces 58 at the outer end of the body portion. The roundedabraded comer surfaces 60 on the inner'end of the body portion assist inpreventing scraping of the wall 40 of the opening. in this manner, theinserts may be mounted in imperfect holes and are firmly secured thereinfrom top to bottom. The inserts are prevented from bending or turning asthey are exposed to lateral and torsional forces, thus minimizingfracture, loosening, and loss of inserts.

Drill bit inserts most frequently fall in the range of about 16 to inchin diameter, with V2 inch and as inch sizes being most frequently used.The inserts of such sizes preferably have at least about 12 sides in thepolygonal body portion, up to about 20 sides. Preferably, l6 to 18 sidesare provided in the l z-inchto %-inch-diamter inserts.

The polygonal body portion, such as the portion 44 of the insert 12,preferably is tapered about one-sixteenth inch per foot of length forshort inserts, e.g., having body portions 44 about three-eighths inch inlength, while a lesser tapering of about one thirty-second inch per footmay be employed for longer lengths, e.g., a length of about three-fourthinch for the body portion 44.

The openings 36, 38 and the like in the working faces of the drill bitbody 16 or other structure may be about 0.003 to 0.0l inch undersizewith respect to the diameter of the insert 44 measured at the outer endof the body portion 44, adjacent to the head portion 48. Relatively widevariation in the size of the opening is permissible, and the openingneed not be true, so that the prior reaming of the opening followingheat treatment may be dispensed with.

The invention thus provides a new and improved insert overcoming priorproblems and providing advantages in mounting the insert in a drill bitso as to minimize fracture ad loss, and a more serviceable drill bitincorporating the insert. The invention also provides a simplifiedmethod of making the insert, which eliminates the need for precisiongrinding and utilizes the normal sintering shrinkage formerly consideredto be a disadvantage. While preferred embodiments of the invention havebeen illustrated and described, it will be apparent that various changesand modifications may be made therein within the spirit and scope of theinvention. It is intended that such changes and modifications beincluded within the scope of the appended claims.

lclaim:

l. A solid wear-resistant sintered metallic carbide insert adapted forforcible insertion into an opening in a working face ofa drill bit whichcomprises a generally polygonal body portion having at least about 12sides extending between opposite ends thereof, and a head portion on oneend of said body portion, the corners formed by said sides being abradedat said ends of said body portion and tapering inwardly towards the endof said body portion opposite to said one end thereof,

said body portion being insertable into said working face opening formounting the body portion therein with said head portion exposed at saidworking face.

2. An insert as defined in claim 1 wherein said metallic carbidecomprises tungsten carbide.

3. An insert as defined in claim 1 wherein said body portion has about12 to sides.

4. An insert as defined in claim 1 wherein said head portion has acircular base substantially tangent to said sides.

5. An insert as defined in claiml including a seat portion having abeveled peripheral edge on said opposite end of said body portion, thecorners formed by said edge being abraded, and said seat portion beingseated on said bit at the base of said working face opening when saidbody portion is mounted therein.

6. A solid wear-resistant sintered tungsten carbide insert adapted forforcible insertion into an opening in a working face of a drill bitwhich comprises a generally polygonal body portion having about 12 to 20sides extending between opposite ends thereof,

a head portion on one end of said body portion, and

a seat portion having a beveled peripheral edge on the opposite end ofsaid body portion,

the corners formed by said body portion sides being abraded increasinglyfrom about the central region of said body portion to said ends thereofand tapering inwardly towards said opposite end of the body portion, andthe comers formed by said seat portion edge being abraded,

said body portion being insertable into said working face opening formounting the body portion therein with said seat portion seated on saidbit at the base of said working face opening and said head portionexposed at said working face.

7. An insert as defined in claim 6 wherein said head portion issubstantially hemispherical with its base substantially tangent to saidsides.

8. A drill bit comprising a body having a working face provided with aplurality of generally circular insert openings extending inwardlytherefrom, and

a plurality of inserts a defined in claim I mounted in said openings,each insert engaging the wall of the opening in which mounted in aninterference fit.

9. A drill bit comprising a body having a working face provided with aplurality of generally circular insert openings extending inwardlytherefrom, and l a plurality of inserts as defined in claim 6 mounted insaid openings, each insert engaging the wall of the opening in whichmounted in an interference fit.

1. A solid wear-resistant sintered metallic carbide insert adapted forforcible insertion into an opening in a working face of a drill bitwhich comprises a generally polygonal body portion having at least about12 sides extending between opposite ends thereof, and a head portion onone end of said body portion, the corners formed by said sides beingabraded at said ends of said body portion and tapering inwardly towardsthe end of said body portion opposite to said one end thereof, said bodyportion being insertable into said working face opening for mounting thebody portion therein with said head portion exposed at said workingface.
 2. An insert as defined in claim 1 wherein said metallic carbidecomprises tungsten carbide.
 3. An insert as defined in claim 1 whereinsaid body portion has about 12 to 20 sides.
 4. An insert as defined inclaim 1 wherein said head portion has a circular base substantiallytangent to said sides.
 5. An insert as defined in claim 1 including aseat portion having a beveled peripheral edge on said opposite end ofsaid body portion, the corners formed by said edge being abraded, andsaid seat portion being seated on said bit at the base of said workingface opening when said body portion is mounted therein.
 6. A solidwear-resistant sintered tungsten carbide insert adapted for forcibleinsertion into an opening in a working face of a drill bit whichcomprises a generally polygonal body portion having about 12 to 20 sidesextending between opposite ends thereof, a head portion on one end ofsaid body portion, and a seat portion having a beveled peripheral edgeon the opposite end of said body portion, the corners formed by saidbody portion sides being abraded increasingly from about the centralregion of said body portion to said ends thereof and tapering inwardlytowards said opposite end of the body portion, and the corners formed bysaid seat portion edge being abraded, said body portion being insertableinto said working face opening for mounting the body portion thereinwith said seat portion seated on said bit at the base of said workingface opening and said head portion exposed at said working face.
 7. Aninsert as defined in claim 6 wherein said head portion is substantiallyhemispherical with its base substantially tangent to said sides.
 8. Adrill bit comprising a body having a working face provided with aplurality of generally circular insert openings extending inwardlytherefrom, and a plurality of inserts a defined in claim 1 mounted insaid openings, each insert engaging the wall of the opening in whichmounted in an interference fit.
 9. A drill bit comprising a body havinga working face provided with a plurality Of generally circular insertopenings extending inwardly therefrom, and a plurality of inserts asdefined in claim 6 mounted in said openings, each insert engaging thewall of the opening in which mounted in an interference fit.